1. Field of the Invention
The present invention relates generally to power supplies and, more specifically, the present invention relates to a switched mode power supply.
2. Background Information
Electronic devices use power to operate. Linear power supplies or adapters are widely used to power electronic products as well as charge batteries used to power mobile products such as for example wireless phones, palm top computers, toys, etc. due to their low cost. However, linear adapters typically include 50-60 Hz transformers, which result in linear power supplies that are very bulky and in efficient.
Switched mode power supplies are commonly used due to their high efficiency and good output regulation to supply power to many of today""s electronic devices. Switched mode power supplies offer the benefits of smaller size, weight, high efficiency and low power consumption at no load in many applications relative to linear power supplies. However, known switched mode power supplies are generally more expensive than their linear power supply counterparts at low power levels, for example below 5 watts, due to the relatively high number and cost of components and the complexity of circuitry. Consequently, linear power supplies are still commonly used in applications having power levels below 5 watts, even though the linear power supplies are bulky and inefficient.
Switched mode power supplies are disclosed. In one embodiment, a power supply includes an energy transfer element having an energy transfer element input and an energy transfer element output, a power switch coupled between the energy transfer element input and a positive input supply rail, and control circuitry coupled to the energy transfer element input and to the power switch. The control circuitry is coupled to switch the power switch in response to a current derived from the voltage at the energy transfer element input. Additional features and benefits of the present invention will become apparent from the detailed description, figures and claims set forth below.